Underbalanced drilling sub

ABSTRACT

A pressure reducing apparatus insertable in a drill string to reduce the fluid pressure immediately surrounding the drill bit and a method for accomplishing pressure reduction. It includes a body with an axial bore, fluid passages in the body communicating with the annulus of the well, and means to divert normal axial drilling fluid flow upwardly through the opened passages. When the fluid is diverted through the passages, a venturi effect is created, thereby reducing the pressure on the drill bit in the area below the passages. The method includes diverting the axial flow of the drilling fluid by restriction of a portion of the inner bore of the well string while the fluid is pumped at a substantially constant rate.

United States Patent [72] Inventor E1vaJ.Scroggins Lafayette, La. [21-] AppLNo. 881,837 [22] Filed Dec.3,1 969 [45] Patented Mar.2, 1971 [73] Assignee Drilling Well Control Inc.

Houston, Tex.

[54] UNDERBALANCED DRILLING SUB 9 Claims, 5 Drawing Figs. [52] U.S.Cl 175/65, 175/317 [51] Int.Cl ..E2lb41/00 [50] FieldofSearch 175/65, 317, 324, 234, 237; 166/224 [56] References Cited UNITED STATES PATENTS 1,619,328 3/1927 Benckenstein l75/317X 2,128,352 8/1938 Creighton 175/65 /fl --a Primary Examiner-Stephen J. Novosad Attorneys-Paul E. Harris and Lee R. Larkin ABSTRACT: A pressure reducing apparatus insertable in a drill string to reduce the fluid pressure immediately surrounding the drill bit and a method for accomplishing pressure reduction. It includes a body with an axial bore, fluid passages in the body communicating with the annulus of the well, and means to divert normal axial drilling fluid flow upwardly through the opened passages. When the fluid is diverted through the passages, a venturi effect is created, thereby reducing the pressure on the drill bit in the area below the passages. The method includes diverting the axial flow of the drilling fluid by restriction of a portion of the inner bore of the well string while the fluid is pumped at. a substantially constant rate.

VIA V1 UNDERBALANCED DRILLING SUB BACKGROUND OF THE INVENTION 1. Field of the Invention i This invention relates generally to an apparatus and method for reducing the fluid pressure in the area immediately surrounding a drill bit. More particularly, the invention relates to an apparatus and method which facilitates drilling operations through hard rock formations by reducing the fluid pressure at the drill bit face.

2. Description of the Prior Art As is well known in the art, bit penetration shows substantial increase with decreasein the hydrostatic pressure exerted by the drilling fluid. The invention accomplishes this objective for hard rock drilling by reducing thefluid pressure at theface of the bit. Devices are known which are directed toward solving the problems, but the prior art has dealt. with increasing the velocity of the annular fluid flow upward to the surface, ridding the drill bit of cuttings more effectively, and preventing the loss of high pressure fluid into low pressure formations. The devices in the prior art require a high flow rate, high capacity pumping system to provide the increased flow rates needed to effect the processes therein described.

The present invention accomplishes all these objects in the area of low pressure created utilizing a substantially constant flow rate of drilling fluid. The present invention, with its constant flow rate, obviates the need for an expensive high capacity pumping system and, in addition, yields greater penetration rates through hard rockformations.

SUMMARY OF THE INVENTION 1 An object of the invention is to provide an improved method and apparatus for drilling through hard rock formations, for example.

The apparatus of the invention for reducing fluid pressure generally surrounding a drill bit includes a body arranged for mounting in a drill string having an axial bore therethrough and having seating means along a first portion thereof and forming along a second portion a plurality of outwardly and upwardly slanted passages'communicating with the annulus of the well. It also includes a means for restricting fluid flow within the bore and arranged for seating with the seating means in the body. The apparatus also includes a slidable means for diverting fluid flow from withinthe bore through the passages at predetermined times. .It also includes means for moving said restricting means to its seated attitude and sliding said slidable means to a fluid diverting position.

Certain embodiments include an integrated tube and plug assembly as the diversion means and flow restricting means whereby predetermined downward sliding movement of the assembly from a suspended attitude within the body simultaneously restricts the axial fluid flow and opens the plural fluid passages to the annulus. In certain otherernbodiments, means are mounted in the body for suspending the tube and plug assembly from an upper portion of the body during normal axial fluid flow conditions.

In other embodiments, orifice inserts are fitted into the plurality of generally upwardly slanted passages which direct the diverted fluid flow in a generally upwarddirection into the annulus.

Still other embodiments include a generally cylindrical tool as moving means for use within the bore of the drill string having a first portion thereof arranged for engaging and disengaging the restricting and diverting means and having a second portion thereof arranged to allow fluid flowthereabout and therethrough during the moving operation and during normal axial flow operations and having a third portion thereof arranged as a fishing neck attachment means to a wireline tools In certain other embodiments, the engaging and disengaging portion of the .tool includes a plurality of resilient fingers open end into which the diverting and restricting means engages.

The method of the invention for varying fluid pressure in the area generally surrounding an operating drill bit includes flowing drilling fluid downwardly through the drill string and drill bit and upwardly through the annulus of the well at a substantially constant rate while rotating the drill string and bit. It also includes the step of reducing the cross-sectional area of a portion of the internal bore of said drill string at predetermined times. The method also contemplates the step of simultaneously diverting a portion of the drilling fluid. generally upwardly and outwardly through bypass points spaced above the drill bit while maintaining reduced fluid flow through the a really reduced portion of the bore whereby the fluid pressure is reduced in the well bore below the bypass points. In certain examples of the method, the flow of drilling fluid through the bypass points is subsequently terminated and normal fluid flow of drilling fluid to the bit is resumed.

BRIEF DEStIRlPTION or THE DRAWINGS The invention may be further understood by reference to the drawings wherein like numerals refer to like parts, and in which:

FIG. 1 is a generally central vertical sectional view of one embodiment of the body and flow restricting and diverting means in normal axial flow attitude.

FIG. 2 is a generally central vertical sectional view of one embodiment of the moving means or shifting tool portion of this invention which is arranged for passage down through the drill string.

FIG. 3 is a generally central vertical sectional view of one embodiment of the invention showing both the body and moving means' in cooperation in diverted or restricted flow at- .titude.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the. numeral 10 refers to the body of the apparatus, the upper end of which is mounted on the lowermost section 11 of a drill string and the lower end of which is connected to a drill bit 12. Body 10 forms an axial bore 13 therethrough to pass drilling fluid from the bore of drill string 11 to drill bit 12, and a generally cylindrical fluid relief enlargement 14 along a portion thereof. Body 10 is also provided with a plurality of fluid passages 15 communicating bore 13 with the annulus of the well. Within each of fluid passages 15 is mounted an orifice insert 150. Each of orifice inserts 15a is held in passage 15 by a retaining ring 15b.

At the lowermost portion of body 10 in bore 13 is a ringshaped'choke seat 16 held in place by the uppermost portion of drill bit 12. An O-ring 25 forms a fluidtight seal between choke seat 16 and body 10. In the uppermost portion of body 10, a substantially ring-shaped blanking sleeve dog assembly 20 is threadably mounted. Blanking sleeve dog assembly 2Q is provided with a plurality of flexible locking dog teeth 20b extending downwardly into the locking dog teeth recess 10a of body 10. Flexible locking dog teeth 20b are provided with releasing shoulders 20a which protrude a short distance into bore 13. Immediately below recess 10a is a blanking sleeve stop 45 which slightly reduces the diameter of bore 13.

Within bore 13 of body 10, an axially slidable tube and plug assembly 26 is provided for restricting and diverting drilling fluid flow. The assembly is comprised of the tubular blanking sleeve 18 and the tubular choke 17. Blanking-sleeve 18 and choke 17 are shown in FIG. 1 in the suspended or axial flow drilling attitude, held by the engagement of locking dog teeth 20]; of blanking sleeve dog assembly 20 in the uppermost portion of body 10 and the blanking sleeve latching shoulder 19.. Immediately below latching shoulder 19 is a blanking sleeve pullout shoulder 27 which contacts blanking sleeve stop 45 to limit the upward axial movement of blanking sleeve 18 in bore 13 of body 11). Blanking sleeve 18 is provided with two O-rings 23 which prevent leakage of drilling fluid from within bore 13 to the annulus through fluid passages 15. Blanking sleeve 18 is also provided with a plurality of fluid circulation passages 22 through which drilling fluid passes around choke 17 while in the suspended attitude.

Choke 17 is threadably mounted to the lowermost portion of blanking sleeve 18 and is provided with a choke fluid passage 21 axially through its center. Choke-17 is also provided with a choke neck 17a for engaging a shifting tool 30 shown in FIG. 2. An O-ring 24 around the lower portion of choke 17 forms a fluidtight seal when choke 17 is seated within choke seat 16.

Shifting tool 30 is arranged for moving tube and plug assembly 26 axially 'within bore 13 of body from the suspended attitude, as shown in FIG. 1, to the seated attitude, as shown in FIG. 3. The uppermost portion of tool 30 is the skirt carrier sub 49 for a pump-down skirt 48. Pump-down skirt 48 insures intimate contact of tool 30 and the inner bore of the drill string (not shown) during the pump-down operation from the wellhead. The upper portion of carrier sub 49 forms a fishing neck 43 for engagement with a wireline tool (not shown). Carrier sub 49 also forms a plurality of fluid entrance ports 32 for flow of drilling fluid throughtool 30. Immediately below carrier sub 49 and skirt 48 is diaphragm sub 50 which houses a circular'rupturable pump-down diaphragm .31 which interrupts fluid flow through tool 30 during the pump-down operation. Diaphragm sub 50 and carrier sub 49 are each threadably mounted on a tubular connector 51 at the lower and upper portions of connector 51, respectively.

The lower end of diaphragm sub 50 is threadably mounted to a hollow body 52 which provides structural support between diaphragm sub 50 and the overshot top sub 53. Ho]- low body 52 also forms upper fluid exit ports 33 and lower fluid exit ports 34 which conduct fluid from bore 13 to fluid passages and choke fluid passages 21, respectively.

Overshot top sub 53 is threadably mounted to the lower portion of hollow body 52 and provides threaded mounting means for a hollow cylindrical overshot shell 39 and a guideway for a grapple bolt 38 to the threaded receptacle for grapple bolt 38 in the lower portion of hollow body 52.

Within overshot shell 39, a ring-shaped grapple finger base 37 is mounted for axial sliding movement on grapple bolt38. Grapple finger base 37 is held in place on grapple bolt 38 by a partially compressed grapple spring 36 from above and a grapple retaining ring 54 from below. Grapple retaining ring 54 is affixed to grapple bolt 38 by a shear pin 44.

Projecting downwardly from grapple finger base 37 within overshot shell 39 are a plurality of grapple fingers 35. Grapple spring 36 holds grapple finger base 37 against grapple retaining ring 54 in a position such that the grapple finger tips 40 are held together at the overshotshell lip 55. Overshot shell 39 of tool is provided with a plurality of fluid bypass slots 56 which allow passage of drilling fluid from bore 13 to choke fluid passage 21 during diverted flow drilling operations.

The tube and plug assembly 26 composed of blanking sleeve 18 and choke 17 assumes two operating attitudes within bore 13 during operation of the invention. In the seated, or diverted flow, attitude, shown in FIG. 3, choke 17 contacts a choke seat 16 in the lower portion of body 10. This attitude provides restricted axial flow of the drilling fluid through choke fluid passage 21 and opens fluid passages 15 to allow fluid flow upward into the annulus of the well through the orifice inserts 15a. The second operating attitude of choke and sleeve as sembly 26 is in a suspended or normal axial flow attitude. in this position, as shown in FIG. 1, the blanking sleeve latching shoulder 19 is held by spring-loaded latching teeth 2% and choke 17 is suspended within fluid relief section 14 of bore 13 within body 11). In this attitude, axial flow of the drilling fluid is maintained through and around choke 17 and directly to drill bit 12 both through the choke orifice 21 and through fluid passages 22 in the lower end of blanking sleeve 18.

Movement of the blanking sleeve 18 and choke 17 assembly axially within bore 13 is accomplished by shifting tool 30 which is put into the drill string at the wellhead. Cooperation of rupturable diaphragm 31 and pump-down skirt 48 interrupts normal fluid flow through entrance ports 32 and out through upper exit ports 33 and lower exit ports 34. Diaphragm 31 and pump-down skirt 48 block the flow of drilling fluid past tool 30 and cause tool 30 to move with the fluid flow from the wellhead through bore 13 of the drill string (not shown) to the situs of underbalanced sub body 11). As tool 30 arrives at the level of body 10, normal axial flow drilling is in process. Blanking sleeve 18 and choke 17 are suspended, as represented in FIG. 1, from latching teeth 21) by latching shoulder 19 of assembly 26. As tool 30 moves downwardly, its first contact in bore 13 is the meeting of choke neck 17a with the spring-loaded grapple finger tips 40 of shifting tool 30. Tool 30 continues to be pushed downward by the action of drilling fluid upon diaphragm 31, further compressing previously partially compressed spring 36 as the grapple finger base 37 is urged upwardly on grapple bolt 38 by the axial force applied to finger tips 40. Grapple fingers 35 move upward relative to overshot s'nell lip 55 into overshot shell 31) and are arranged to spring radially outward, thereby permitting the finger tips 40 to ride over choke neck 17a. After overshot shell lip 55 passes choke neck 17a, grapple finger tips 40 are urged or cammed radially inward around choke neck 17a by the action of grapple spring 36. Grapple fingers 35 hold choke neck 17a firmly just inside overshot shell 39 by the cooperation of overshot shell lip 55 and grapple finger tips 40.

After grapple fingers 35 have engaged choke neck 17a, 17a, shifting tool 30 continues its downward movement a short distance, at which time the lower shoulder 41 of hollow body 52 contacts the releasing shoulders 20a, disengaging latching teeth 20b from blanking sleeve 18. As latching teeth 20b release blanking sleeve latching shoulder 19, sleeve and choke assembly 26 is freed for downward axial movement. Tool 30 and blanking sleeve and choke assembly 26 move axially downward until choke 17 seats in choke seat 16 of body 11). The restricted flow attitude of the device is now established, as shown in FIG. 3.

Blanking sleeve 18, which initially covered fluid passages 15, has been moved downward to open fluid passages 15. Drilling fluid is pumped down bore 13 through entrance ports 32 of tool 30, creating a pressure on diaphragm 31 until the rupture pressure is exceeded. After diaphragm 31 is ruptured, the drilling fluid flows through the hollow body 52 of tool 31) and exits through upper exit ports 33 into fluid passages 15 of body 10 and upward to the annulus, as well as down through lower exit ports 34, through fluid bypass slots 56 of overshot shell 39, through choke orifice 21, and finally to drill bit 12. Thus the axial fluid flow to drill bit 12 is reduced to that portion of the former normal axial flow which can be forced through choke orifice 21. The remainder of the flow is directed upwardly and outwardly through plural fluid passages 15 into the annulus through orifice inserts 15a. This diverted upward flow accomplishes pressure reduction by venturi effect on that portion of the annulus below fluid passages 15.

When the hard rock formation has been penetrated and normal drilling operations are again needed, shifting tool 31) and blanking sleeve 18 and choke 17 assembly are raised to the suspended, or normal axial flow, attitude. This is accomplished by attaching a wireline tool (not shown) which has been lowered through bore 13 of the drill string and attached to the fishing neck 43 of skirt carrier sub 49 of shifting tool 31). Shifting tool 30 is slowly elevated, bringing with it the engaged blanking sleeve 18 and choke 17 assembly, until blanking sleeve latching shoulder 19 is reengaged by latching teeth 20b of body 10. Tool 31) is then jarred upwardly with enough force to shear shear pin 44 which has held grapple fingers 35 within overshot shell 39 by means of retaining ring 54. Grapple finger tips 41) then extend downwardly below overshot shell 39. The wireline tool (not shown) attached to the shifting tool 31) is then withdrawn and blanking sleeve 18 and choke 17 remain in body 11) as grapple fingers 35 disengage from choke neck S 17a. Blanking sleeve 18 and choke 17 are held within body by blanking sleeve stop 45 of body 10.

The wireline tool (not shown); with shifting tool at tached, is then withdrawn at the wellhead. After insertion of a new rupturable diaphragm 31 and shear pin 44 and reassembly of thegrapple finger system, shifting tool 30 can be used to perform another cycle of shifts of the blanking sleeve 18 and choke l7 assembly from axial flow to restricted flow to axial flow.

The invention incorporates the advantage over the prior art of constant drillingfluid flow rate during reduced pressure drilling. When reduced pressure drilling is desired, the operator merely inserts the shifting tool of this invention into the bore of the drill string at the wellhead. The shifting tool has a rupturable diaphragm which causes the tool to move with the flow of the drilling fluid until itrea hes that portion of the drill for hard rockdrilling is another advantage of the invention.

No extended shut-down period or string-pulling operation is required.

After the hard formation has been penetrated, normal drilling can be resumed by readjusting the choke. of the invention by means of a wireless tool, again omitting the necessity of pulling the drill string. 1 t

An additional advantage of the upward slanting passages is that the fluid forced upward in the annulus provides a downward thrust on the bit, thereby increasing contact of the bit with bottomhole, providing improved drilling results. i

Thus, it can be seen that a rapid and economical method of reducing pressure in thearea of a drill bit has been shown. This description of the combination is to be construed as illustrative onlysince other embodiments of the invention will be apparent to those skilled in the art in view of this description.

Iclaim:

1. In an apparatus for reducing fluid pressure generally surrounding a drill bit during drilling operations, the combination comprising:

a body arranged for mounting in a drill string and having an' axial bore arranged for flow of drilling fluid therethrough, and said body having seating means along a first portion restricting means and said diversion means include an integrated tube and plug assembly, whereby predetermined downward sliding movement of said assembly from a suspended attitude within said body simultaneously restricts said axial fluid flow and opens said plurality of fluid passages to the annulus.

3. The invention as claimed in claim 2 including means mounted in-said body for suspending said tube and plug as sembly from an upper portion of said body during normal axial fluid flow conditions.

4. The invention as claimed in claim 3 wherein the tubular portionof said tube and plug as'semlbly forms a plurality of fluid bypass passages, whereby axial'fluid flow is maintained generally through said bore during nonnal axial flow drilling operations.

5. The invention as claimed in claim 1 wherein said plurality of enerall u wardl slanted ass es formed b said bod are each ltte rl witli an orifice in sert which ti irects said diverted fluid flow in a generally upward direction into said annulus.

6. The invention as claimed in claim 1 wherein said moving means includes a generally cylindrical tool arranged for i ing and disengaging portion of said tool includes a plurality of resilient fingers mounted on an axially slidable and of said bore and a plurality of generally outwardly and upwardly slanted passages communicating between said bore and the annulus of the well at a point generally above said seating means;

means mounted within said bore for seating with said seating means for restricting fluid flow therethrough' at downwardly presprung base enclosed within an overshot shell,

said shell having an open end into which said diverting and restricting means engages.

'8. In a method for varying fluid pressure in the area generally surrounding an operating drill bit suspended on a drill string in a well bore, the combination of steps comprising: flowing drilling fluid downwardly through said drill string and drill bit and upwardly through the annulus of the well at a substantially constant rate while rotating said drill string and bit; reducing the cross-sectional area of a portion of the internal bore of said drill string at predetermined times; simultaneously diverting a portion of said drilling fluid generally upwardly and outwardly through bypass points spaced above said drill bit whilemaintaining reduced fluid flow through said a really reduced portion of said bore; and whereby the fluid pressure is'reduced in said'well bore below said bypass points 9. The invention as claimed in claim 8 including subsequently terminating said flow of drilling fluid through said bypass points and resuming normal fluid flow of drilling fluid to said bit. v 

2. The invention as claimed in claim 1 wherein said flow restricting means and said diversion means include an integrated tube and plug assembly, whereby predetermined downward sliding movement of said assembly from a suspended attitude within said body simultaneously restricts said axial fluid flow and opens said plurality of fluid passages to the annulus.
 3. The invention as claimed in claim 2 including means mounted in said body for suspending said tube and plug assembly from an upper portion of said body during normal axial fluid flow conditions.
 4. The invention as claimed in claim 3 wherein the tubular portion of said tube and plug assembly forms a plurality of fluid bypass passages, whereby axial fluid flow is maintained generally through said bore during normal axial flow drilling operations.
 5. The invention as claimed in claim 1 wherein said plurality of generally upwardly slanted passages formed by said body are each fitted with an orifice insert which directs said diverted fluid flow in a generally upward direction into said annulus.
 6. The invention as claimed in claim 1 wherein said moving means includes a generally cylindrical tool arranged for passage through the bore of a drill string, said tool having along a first portion thereof means arranged for engaging and disengaging said restricting means and said diverting means and forming along a second portion thereof a plurality of fluid passages arranged to allow fluid flow about and through said tool during the moving operation and normal axial flow operations and having along a third portion thereof a fishing neck arranged for coupling with a wireline tool.
 7. The invention as claimed in claim 6 wherein said engaging and disengaging portion of said tool includes a plurality of resilient fingers mounted on an axially slidable and downwardly presprung base enclosed within an overshot shell, said shell having an open end into which said diverting and restricting means engages.
 8. In a method for varying fluid pressure in the area generally surrounding an operating drill bit suspended on a drill string in a well bore, the combination of steps comprising: flowing drilling fluid downwardly through said drill string and drill bit and upwardly through the annulus of the well at a substantially constant rate while rotating said drill string and bit; reducing the cross-sectional area of a portion of the internal bore of said drill string at predetermined times; simultaneously diverting a portion of said drilling fluid generally upwardly and outwardly through bypass points spaced above said drill bit while maintaining reduced fluid flow through said a really reduced portion of said bore; and whereby the fluid pressure is reduced in said well bore below said bypass points.
 9. The invention as clAimed in claim 8 including subsequently terminating said flow of drilling fluid through said bypass points and resuming normal fluid flow of drilling fluid to said bit. 